The invention relates to improvements in methods of making, assembling and operating an apparatus which can be utilized to damp vibrations in the power trains of motor vehicles, for example, between the crankshaft or camshaft of an internal combustion engine and the input shaft of a manually shiftable or automated transmission. The invention also relates to improvements in torsional vibration damping apparatus which can be utilized with advantage in the power trains of motor vehicles.
More particularly, the invention relates to improvements in methods of making torsional vibration damping apparatus of the type wherein input and output members are rotatable with and relative to each other about a common axis, wherein the angular movements of the input or output member relative to the other member are opposed by at least one damper, and wherein the input and output members are centered relative to each other by radial and/or axial (thrust) bearings.
Published German patent applications Serial Nos. 35 15 928 A1 and 34 11 092 A1 disclose torsional vibration damping apparatus wherein rotation of coaxial primary and secondary flywheels relative to each other is opposed by a damper employing energy storing devices in the form of coil springs. A journal bearing is provided to center and locate the flywheels relative to each other radially as well as in the direction of their common axis.
It has been found that such centering means which act as radial and simultaneously as axial bearings exhibit a number of drawbacks. One of the reasons is that the parts of the combined radial and axial bearing must be finished and assembled with minimal tolerances which contributes to the cost of the centering means and of the entire torsional vibration damping apparatus. In fact, the tolerances are frequently so narrow that they can be defined as so-called negative tolerances, i.e., the parts which are to rotate and/or move axially relative to each other can carry out the required movements only by overcoming a pronounced resistance to axial and/or angular movement relative to one anoter. In other words, the frictional resistance which is encountered by the primary and secondary flywheels of a torsional vibration damping apparatus embodying axial and/or radial bearings of the above outlined character operates in parallel with the aforementioned coil springs of the damper.
The combined resistance to rotation of the primary and secondary flywheels in such torsional vibration dampers is often excessive for satisfactory operation of the apparatus in the power trains of numerous types of motor vehicles, especially during certain stages of operation of the vehicles. For example, the combined resistance of the aforediscussed bearings and of the springs of a damper in a torsional vibration damping apparatus is often excessive when the engine is idling, i.e., when the transmission is in neutral gear. Thus, the engine continues to transmit vibratory movements to the input element of the transmission, and this often entails the generation of undesirable noise (such as rattling) in the transmission and/or in certain other constituents of the power train.
Another drawback of presently known and utilized torsional vibration damping apparatus which employ combined axial and radial bearings with parts which are to be assembled with minimal or even negative tolerances is that, due to unavoidable departures from ideal tolerances, the tolerances which actually develop during assembly of a conventional torsional vibration damping apparatus and/or during installation of such apparatus in a power train are highly unpredictable and can vary from apparatus to apparatus or from power train to power train. In other words, the likelihood of ensuring that the quality of the centering action of combined radial and axial bearings in a long (or even short) series of power trains will remain within a desired or prescribed range is rather remote.
On the other hand, attempts to avoid excessively narrow tolerances (or even negative tolerances) and the resulting pronounced friction between the component parts in the centering means (and/or between such component parts and the input and output members of a torsional vibration damping apparatus) by simply increasing the radial tolerances would invariably result in equally unsatisfactory excessive play between neighboring relatively movable parts right from the time of initial assembly of a torsional vibration damping apparatus and its incorporation into a power train. This could result in pronounced wobbling of parts (such as primary and secondary flywheels) in a new apparatus with attendant pronounced or excessive wear and generation of noise within a range (i.e., of an intensity) which is unacceptable to the occupant or occupants of a motor vehicle.
An object of the invention is to provide a novel and improved method of making and assembling torsional vibration damping apparatus with tolerances which are more predictable and hence more acceptable than those developing in heretofore known torsional vibration damping apparatus.
Another object of the invention is to provide a method which ensures that the noise generated by the parts of an apparatus which is assembled and installed in accordance with such method is much less bothersome than the noise generated by conventional torsional vibration damping apparatus.
A further object of the invention is to provide novel and improved centering means for use in a torsional vibration damping apparatus which is constructed, assembled and installed in accordance with the above outlined method.
An additional object of the invention is to provide a method which renders it possible to furnish highly satisfactory centering means for use in torsional vibration damping apparatus at a cost which is much less than the cost of conventional apparatus wherein the centering means are assembled with negligible or even negative tolerances.
Still another object of the invention is to provide a method which renders it possible to produce short or long series of centering means with highly satisfactory and highly predictable tolerances between parts which are called upon to rotate and/or to move axially relative to each other.
A further object of the invention is to provide a torsional vibration damping apparatus which is constructed and assembled in accordance with the above outlined method.
Another object of the invention is to provide a power train which embodies the above outlined torsional vibration damping apparatus, for example, between the output shaft of an internal combustion engine and the friction clutch which transmits torque to the input shaft of the transmission.
An additional object of the invention is to provide novel and improved procedures for the establishment of satisfactory tolerances between the primary and secondary flywheels of so-called dual-flywheel torsional vibration dampers between the engines and the clutches of power trains in motor vehicles.
Still another object of the invention is to provide a torsional vibration damping apparatus with novel and improved primary and secondary flywheels.
A further object of the invention is to provide a torsional vibration damping apparatus whose operation is exceptionally quiet and smooth even though the constituents of the bearings in such apparatus need not be machined and/or otherwise treated to an exceptionally high degree of precision finish.
An additional object of the invention is to provide a novel and improved sleeve for use in the radial bearing of the above outlined torsional vibration damping apparatus.
One feature of the invention resides in the provision of a method of making an apparatus which is to be utilized as a means for damping torsional vibrations and comprises at least one input member, at least one output member which is rotatable with an relative to the output member about a common axis, and a centering means or unit or system including a bearing which is interposed between the input and output members to center such members at least against excessive movements relative to each other radially of the common axis and comprises a sleeve having external and internal surfaces. The improved method comprises the steps of establishing an at least substantially clearance free fit between one surface of the sleeve and a complementary surface of one of the input and output members, calibrating the diameter of the other surface of the sleeve, and thereafter juxtaposing the other surface of the sleeve with a complementary surface of the other of the input and output members.
One of the complementary surfaces can constitute an external surface of an extension of the respective one of the input and output members.
As a rule, one of the complementary surfaces overlies the other complementary surface as seen in the direction of the common axis of the input and output members.
The one surface can constitute the external surface of the sleeve, and the calibrating step then preferably includes introducing a male calibrating tool into the sleeve.
If the one surface is the internal surface of the sleeve, the calibrating step can include introducing the sleeve into a female calibrating tool.
The calibrating step can include hardening and/or densifying the sleeve in the region of the other surface.
In addition to or in lieu of hardening and/or densifying, the calibrating step can include imparting to the other surface of the sleeve a roughness in the range of between Rz 1.6 and 6 micrometers, particularly between Rz 3 and 5 micrometers.
It is also within the purview of the invention to impart to the other surface of the sleeve a roughness of less than 0.8 micrometer, particularly in the range of between 0.3 and 0.6 micrometer.
Still further, the calibrating step can include reducing the out-of-roundness of the internal surface of the sleeve provided, of course, that the internal surface was out of round, or excessively out of round, prior to the calibrating step.
The calibrating step can also comprise (or it can be preceded by) the step of lubricating the other surface of the sleeve. Such lubricating step can include contacting the other surface of the sleeve with oil. Alternatively, or in addition to the just discussed lubrication, the calibrating step can include lubricating a calibrating surface of a calibrating tool, and contacting one surface (particularly the outer surface) of the sleeve with the calibrating surface of such tool.
If the other surface is the internal surface of the sleeve, the calibrating step can include inserting into the sleeve a male calibrating tool having a maximum outer diameter which exceeds the desired or expected or optimum diameter of the internal surface of the sleeve by a value in the range of between 0.03 and 0.15 millimeter, particularly between 0.06 and 0.12 millimeter. Such calibrating step preferably results in an increase of the diameter of the internal surface of the calibrated sleeve by between 5 and 40% of the difference between the maximum outer diameer of the male calibrating tool and the diameter of the internal surface of the sleeve prior to the calibrating step. A presently preferred increase of the diameter of the internal surface of the sleeve is between 10 and 25%.
If the other surface is the internal surface of the sleeve, the calibrating step can include inserting into the sleeve a male calibrating tool in the direction of the common axis of the input and output members (such axis coincides or should coincide with the axis of the sleeve), and thereupon extracting the male calibrating tool from the sleeve in the direction of such axis. The arrangement can be such that initial insertion of the male calibrating tool takes place in a first direction, and the extracton of the tool (this actually amounts to a renewed calibration) takes place in a second direction counter to the first direction.
If the other surface is the external surface of the sleeve, the calibrating step can include slipping onto the external surface of the sleeve a female calibrating tool in the axial direction of the sleeve, and thereupon retracting the female calibrating tool off the external surface of the sleeve in the axial direction of the sleeve.
At least a part of the calibrating step can take place simultaneously with the first step (of establishing the at least substantially clearance-free fit). The step of establishing an at least substantially clearance-free fit can include utilizing a first part of a combined fitting and calibrating tool, and the calibrating step then comprises (or can comprise) utilizing a second part of the combined fitting and calibrating tool. If the one surface is the external surface of the sleeve, the step of utilizing the second part of the combined fitting and calibrating tool can include causing the second part to enter the sleeve axially in a first direction prior to the step of establishing an at least substantially clearance-free fit so that a calibrating portion of the second part of the combined fitting and calibrating tool is confined in a portion of the internal surface of the sleeve which is to be calibrated, and extracting the second part of the combined fitting and calibrating tool from the sleeve in a second direction counter to the first direction and subsequent to the step of establishing the at least substantially clearance-free fit.
If the apparatus is of the type wherein the sleeve of the centering means has a slot extending all the way between its ends (such as an axially parallel slot or a helical slot) and being bounded by axially parallel or helical faces, the step of establishing the at least substantially clearance-free fit can comprise inserting the external surface of the slotted sleeve into the complementary internal surface of the respective one of the input and otput members to thus urge the axially parallel or helical faces which bound the slot against each other and to simultaneously urge the external surface of the sleeve against the complementary internal surface of the respective (input or output) member.
If the sleeve is provided with an external collar at one of its axial ends, the method can further comprise the step of locating the collar between confronting radial surfaces of the input and output members to thus determine (i.e., fix) the axial positions of the input and output members relative to each other. Such method can further comprise the step of making the collar of one piece with the one end of the sleeve, and/or the step of imparting to the collar an at least substantially circular outline.
The method can also comprise the step of imparting to the sleeve the shape of a cylinder.
Still further, the method can comprise the step of coating at least one of the internal and external surfaces of the sleeve with a friction reducing material.
The step of establishing the at least substantially clearance-free fit can comprise providing one of the input and output members with an axial extension close to the common axis of the input and output members, and inserting one of the extension and the sleeve into the other of these parts. The inserting step can comprise establishing a press fit between the extension and the sleeve. Alternatively, the inserting step can include establishing between the extension and the sleeve a sliding fit which permits the extension and the sleeve to turn relative to each other about the common axis of the input and output members in the fully assembled apparatus. The aforementioned providing step can include deforming a portion of the respective (input or output) member to thus provide the extension on the deformed member. The deforming step can constitute a deep drawing step.
The method can further comprise the steps of providing one of the input and output members with a socket and providing the other of these members with an extension. In accordance with this method, the step of establishing the at least substantially clearance-free fit can include a first inserting step of introducing the sleeve or the extension into the other of these parts, and the method can further comprise a second inserting step which involves introducing the other of the parts including the sleeve and the extension into the socket upon completion of the calibrating step. The first inserting step can include establishing a tight fit between the extension and the sleeve, and the second inserting step can include establishing a tight fit between a surface surrounding the socket and the other of the parts including the sleeve and the extension.
If the method involves the making of an apparatus wherein the input and output members respectively comprise primary and secondary flywheels, such method can further comprise the steps of connecting the primary flywheel to a rotary output component of a prime mover in a power train of a motor vehicle (e.g., to the camshaft or to the crankshaft of the internal combustion engine in the power train), connecting the secondary flywheel with a rotary input component of a transmission in the power train, and providing the power train with a damper which opposes rotation of the flywheels relative to each other. Such method can further comprise the step of utilizing the sleeve as a part of a combined radial and axial or thrust bearing for the flywheels. The step of connecting the secondary flywheel with the rotary input component of the transmission can include providing the power train with an engageable and disengageable clutch (such as a friction clutch) arranged to receive torque from the secondary flywheel and to rotate the input component when it assumes an at least partially engaged condition.
Another feature of the invention resides in the provision of an apparatus for damping torsional vibrations, e.g., in the power train of a motor vehicle. The improved apparatus comprises an input member and an output member which is rotatable with and relative to the input member about a common axis. The input and output members have annular surfaces which overlie each other as seen in the direction of the common axis, and the apparatus further comprises resilient means for yieldably opposing rotation of the input and output members relative to each other, and means for centering the input and output members relative to each other. The centering means comprises a radial bearing having a sleeve with an internal surface complementary to and adjacent to one of the annular surfaces, and an external surface complementary and adjacent to the other of the two annular surfaces. The centering means further comprises an axial or thrust bearing which is interposed between the input and output members. The sleeve is located at a first radial distance from the common axis, and the thrust bearing is located at a different second radial distance from such axis.
The second radial distance can be less than the first radial distance. The input and output members of such apparatus can respectively comprise primary and secondary flywheels, and the apparatus can further comprise means for connecting the primary flywheel with a rotary output component of a prime mover in a power train of a motor vehicle. The secondary flywheel of such apparatus is connectable with a rotary input component of a transmission in the power train, and such secondary flywheel can be provided with at least one opening affording access to the connecting means. The at least one opening can be located at a third radial distance from the common axis; the third radial distance can be greater than the second radial distance but less than the first radial distance.
The thrust bearing can comprise at least one annular member which extends radially of the common axis and has a surface slidably contacting (directly or indirectly) one of the input and output members.
At least one of the annular and complementary surfaces can be provided with a smooth finish; for example, the at least one surface can be burnished or it can be treated in a lathe or another turning machine.
It is further possible to provide at least one layer of a suitable friction reducing material on at least one of the annular and complementary surfaces; for example, such at least one layer can contain a sintered friction reducing material which can be rolled onto the at least one surface. The at least one layer of friction reducing material can contain porous bronze, and such layer can further contain a lubricant.
The sleeve of the radial bearing can consist of a metallic sheet material, e.g., of sheet aluminum or sheet steel stock.
The thrust bearing can comprise a collar located in a plane which is at least substantially normal to the common axis of the input and output members received between neighboring radial surfaces of such members. This thrust bearing preferably further comprises at least one layer of friction reducing material which is provided on or at least the collar adjacent at least one of the two radial surfaces.
The sleeve of the radial bearing can constitute a converted blank of sheet material.
Furthermore, at least a portion of at least one of the input and output members can be made of a suitable sheet material.
As already mentioned above, the input and output members can respectively comprise primary and secondary flywheels, and the apparatus can further comprise an engageable and disengageable clutch which is arranged to receive torque from the primary flywheel (preferably by way of the secondary flywheel). The clutch normally comprises a clutch spring, and the apparatus can further comprise means for biasing the thrust bearing in the direction of the common axis of the input and output members (i.e., of the primary and secondary flywheels). Such apparatus further comprises means for disengaging the clutch, and such disengaging means can comprise a bearing device (e.g., an antifriction ball or roller bearing) arranged to disengage the clutch by way of the clutch spring. Such bearing device can constitute the aforementioned means for biasing the thrust bearing. The clutch spring can include or constitute a diaphragm spring.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved torsional vibration damping apparatus itself, however, both as to its construction and the mode of making, assembling and utilizing the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.